on my Mustangs I've tried:
1) Thomastik JF344
2) D'Addario Chromes ECB81M
3) Fender 9050L
4) La Bella 760FL MUS
5) GHS Precision Flat 3120
6) Pyramid Gold short scale
what can I say is that:
1) Thomastik are what we all know, modern sounding flats with strong midrange in the upper side of the mid-register. low tension, flexible,
2) Chromes are bright and scooped, with strong highs and lows
3) Fender are bright and strong on the hi-mids, less on the low mids
4) La Bella are thumpy with zero sustain (the E string handles an octave note and dies

), and after a while they makes the bass sound like it has the tone closed
5) GHS P flats are strong on the low mids and tight lows, woody tone well defined in the mix,
6) Pyramid are similar to GHS, but with less hi-mids, so they mud a bit.
my favourite are the GHS, and the least the La Bella. I couldn't use them in a band, unless I used a pick.